An amino acid such as L-glutamic acid and L-aspartic acid is important as a neurotransmitter in a central nervous system for activating a nerve cell. However, excessive accumulation of these excitatory amino acids outside a cell is thought to cause loss of nerve and motion functions seen in various cerebro-neurological diseases such as Parkinson's disease, senile dementia, Huntington's chorea, and epilepsia, as well as at anoxia, ischemia, hypoglycemia state, or head or spinal cord damage.
It is known that the activity of the excitatory amino acid on a central nervous cell acts via a glutamic acid receptor present on a nerve cell, and a glutamic acid receptor antagonist is thought to be useful as a remedy for the aforementioned diseases and symptoms, and for example, as an anti-epileptic drug, a preventive for ischemic brain injury, or a drug for anti-Parkinsonism.
The NMDA receptor which is one kind of glutamic acid receptors is composed of two subunits of NR1 and NR2, and there are further 4 kinds (NR2A, 2B, 2C, 2D) of subfamilies in the NR2 subunit. It is said that the NR1/NR2A receptor is exclusively involved in memory formation or learning acquisition, and the NR1/NR2B receptor is involved in transmission of neurodegenerative cell death or pain at ischemia. Therefore, a drug exhibiting high affinity for the NR1/NR2B receptor has a high possibility that it becames an effective analgesic having little side effect.
Compounds similar to the present compounds are described in the Patent Literature 1 to 20 and non-Patent Literature 1, but the compound related to the present invention is described in none of them.
[Patent Literature 1]
    International Publication WO 03/057688[Patent Literature 2]    International Publication WO 02/068409[Patent Literature 3]    International Publication WO 02/080928[Patent Literature 4]    International Publication WO 02/40466[Patent Literature 5]    Japanese Patent Application Laid-Open (JP-A) No. 11-147872[Patent Literature 6]    JP-A No. 1-079151[Patent Literature 7]    JP-A No. 2-169569[Patent Literature 8]    International Publication WO 2003/076420[Patent Literature 9]    International Publication WO 2003/010159[Patent Literature 10]    International Publication WO 2006/010968[Patent Literature 11]    International Publication WO 2006/010964[Patent Literature 12]    International Publication WO 2003/053366[Patent Literature 13]    International Publication WO 03/084948[Patent Literature 14]    International Publication WO 2002/051806[Patent Literature 15]    International Publication WO 2001/007436[Patent Literature 16]    International Publication WO 86/00899[Patent Literature 17]    Switzerland Patent Application Publication No. CH460016 [Patent Literature 18]    Switzerland Patent Application Publication No. CH460017 [Patent Literature 19]    U.S. Pat. No. 3,538,089[Non-Patent Literature 1]    Farmaco 1989, vol. 44, No. 5, p. 227-255